Circuit-switched network architectures, such as those based on synchronous optical network (SONET) or synchronous digital hierarchy (SDH) standards, were originally designed to support voice traffic using dedicated fixed-bandwidth connections. Although such networks are advantageous in that they incorporate substantial reliability and protection mechanisms, their primary disadvantage has been a lack of bandwidth efficiency.
Packet-switched network architectures, which include those based on asynchronous transfer mode (ATM) or Internet protocol (IP) standards, have traditionally been much better able than circuit-switched architectures to handle data traffic. Since data traffic is inherently bursty, it leads to underutilization of the fixed-bandwidth connections of conventional circuit-switched networks. Packet-switched network architectures provide the benefits of statistical multiplexing, which allows for better handling of bursty data traffic.
Recently, virtual concatenation (VC) and link capacity adjustment scheme (LCAS) protocols have been developed which allow more efficient use of the existing fixed-bandwidth connections associated with circuit-switched SONET/SDH network infrastructure. For example, these protocols are utilized in transmission of Ethernet over SONET (EoS) data traffic over metropolitan networks, and in numerous other data transmission applications. The VC and LCAS protocols are described in greater detail in, for example, ITU-T standards documents G.707 and G.7042, respectively, both of which are incorporated by reference herein.
Virtual concatenation generally allows a given source node of a network to form a virtually-concatenated group (VCG) which includes multiple members each associated with a corresponding data stream. The different data streams may then be transmitted over diverse routes through the network from the source node to a given destination node, also referred to herein as a sink node. The destination node recombines the streams to reconstruct the original VCG.
The LCAS protocol enhances the basic virtual concatenation functionality described above by allowing so-called “hitless” addition and deletion of members from a VCG, that is, addition and deletion of members without the introduction of errors into the transmitted data. The LCAS protocol also enables a VCG to operate at a reduced capacity after the failure of routes associated with one or more members, by allowing the temporary removal of members associated with failed routes from the VCG.
The above-cited U.S. patent application Ser. No. 10/446,220 and Ser. No. 10/745,881 provide additional performance improvements beyond those associated with the conventional VC and LCAS protocols.
It is often desirable, when implementing VC or LCAS related techniques, to provide compensation for differential delays of the diverse routes over which the various members of a VCG are transmitted. Providing such a capability in conventional practice typically requires that each network node be configured to include a differential delay buffer. Since a given destination node may receive different diversely-routed members at different times, the differential delay buffer is used to store member data until all members are received and the original data stream can be properly reconstructed.
Additional details regarding conventional aspects of differential delay compensation can be found in, for example, G. Garg et al., “Managing Differential Delay in SONET Architectures,” EE Times, January 2002, which is incorporated by reference herein.
In provisioning a set of diverse routes for members of a VCG, it is important to have an accurate estimation of link delays. For example, link delay determination is essential for proper implementation of Quality of Service (QoS) in delay-sensitive applications such as voice transmission. A given provisioned VCG circuit with a non-zero differential delay will require the destination node to hold the faster arriving members in memory until the slower ones arrive. Holding these members consumes differential delay buffer space at the sink node. Since many network nodes have only a small amount of buffer memory, the onus is on the routing algorithm to ensure that the VCG circuit is not set up along routes where members will experience more differential delay than can be accommodated by the corresponding nodes. Thus, not all sets of diverse routes between a given pair of nodes are feasible, since one or more of the sets of diverse routes could result in a differential delay that cannot currently be compensated by the available buffer space.
It is therefore apparent that accurate and efficient link delay determination can facilitate the provisioning of diverse routes for VCG members. Unfortunately, conventional link delay determination techniques fail to provide a sufficient level of efficiency and accuracy, particularly in the VCG provisioning context. The link delay in a SONET/SDH network is typically comprised of two components, namely, propagation delay, which is dependent upon the span length and speed of light in the transmission medium, and equipment delay, which is introduced by various types of network equipment in the span, such as amplifiers, regenerators, etc. In conventional practice, the span length and its associated transmission properties are usually not known with precision. This forces service providers either to approximate such parameters or to utilize a proportional cost assignment approach when performing QoS routing.
Accordingly, a need exists for improved techniques for determining link delays in networks carrying virtually-concatenated data traffic.